Carl moldenhatjer



' UNITED STATES PATENT Enron-'4' CARL MOLDENHAUER, OF FRANKFORT-ON-THEMAIN, GERMANY.

PRECIPITATING PRECIOUS METALS OF THEIR SOLUTIONS.

SPECIFICATION forming part of Letters Patent No. 512,046, dated January 2,18i34.

Application filed August 19, 1893- Serial No. 483,574. (No specimens.)

To all whom it may concern.-

Be it known that I, CARL MOLDENHAUER, a sub ect of the Emperor of Germany, and a resldent of Frankfort-on-the-Main, Germany, have invented certain new and useful Improvements in Precipitating Precious Metals out of their Solutions, of which the following is a specification.

The process consists in the use of aluminum for the industrial precipitation of gold and other precious metals out of cyanide-solutions 1n thepresence of free alkali or earth alkali.

Hitherto zinc has been used for the industrlal precipitation of gold out of the cyanide solutions which have been obtained by dissolving the gold from its ores by means of a solution of cyanide of potassium. But when used for the purpose in question the zinc shows considerable disadvantages I have found that these disadvantages are avoided if aluminum is used for the purpose in question. While zinc enters into combination with the bound or free cyanide of alkali contained in the1 cyanide-solutions according to the formu a:

6Au+12KGy+3O+6H O= 6AuKOy +6KHO+3H Q If to this cyanuret-of-gold-solution, which contains free alkali, aluminum is added, the following reaction takes place:

The free cyanic acid which is formed according to this formula combines at once with the free alkali present to form cyanide of potas sium according to the following formula:

By the action of aluminum therefore the cyanide of potassium which has been used for dissolving the gold out of its ores, is regenerated, which is not the case when zinc is used. But the zinc does not confine itself to enter into combination with the cyanogen of the cyanuret-of-gold-solution, but it attacks also the free cyanide of potassium which is still contained in the solution, whereby this free cyanide of potassium is consumed to a great part, which is also not the case with aluminum.

Thesefacts are, for the use of the waste solution for a new extraction of gold, of great importance inasmuch as by this the whole cyanogen of the regenerated and remaining free cyanide of potassium can at once be used anew, while the solutions which are obtained by the use of zinc are not of so great an advantage. Trials for regenerating them have often been made, but they are comparatively dear. Therefore it is clear that by the use of aluminum a great saving of cyanide of potassium is attained. In fact only that part of cyanide of potassium needs to be replaced,which has been lost mechanically and which has been decomposed by alien influences. To this great and essential advantage of the aluminum some other ones join. The aluminum is much less subject to oxidation than the zinc, so that it can be sent from the place of its production in that form in which it has to be used for the precipitation, while in the use of zinc it is regarded as a great advantage to bring it into the required form at the place of its use and immediately before its use. For the same reason also the repeated use of the aluminum for continued precipitations is admissible. Finally for the precipitation of one and the same quantity of precious metal four times less aluminum than zinc is required.

' It is knownto me that aluminum has already I do not confine myself to any special form in which the aluminum has to be used, as it can be used in any suitable form.

What I claim, and wish to be secured by United States Letters Patent, is

Precipitating gold and other precious metals out of their cyanide-solutions by treating the latter with aluminum in the presence of a free alkali as and for the purpose set forth.

In testimony that I claim the foregoing as my invention I have signed my name in pres- I ence of two subscribing witnesses.

CARL MOLDENHAUER. Witnesses:

CARL FEHR, FRANK H. MASON. 

